The American inventor Wilson Greatbatch, who has died aged 92, devised the first practicable implantable heart pacemakers. They have saved thousands of lives and improved many more, and he continually sought to refine them.

While building a device for recording heart rhythms at the University at Buffalo, New York state, in 1956, Greatbatch inadvertently fitted it with an unsuitable resistor. As a result, it produced intermittent electrical impulses instead of oscillating ones. He had long believed that electrical stimulation could compensate for a failing heart, but felt it would be impossible to build a device small enough to be workable. It now came to him that a device might after all be buildable, and he determined to do so.

In two years he had miniaturised a device down to two cubic inches, and in May 1958 surgeons implanted it into a dog, whose heartbeat it demonstrably controlled. Pacemaker research was going on in other centres in the US and Europe, and the same year Swedish surgeons implanted the first pacemaker into a human. It failed after three hours. A second device lasted two days, and further improvement continued slowly.

Greatbatch left his job at Buffalo to develop his ideas in his garden shed, using his $2,000 savings. He collaborated with William Chardack at the Buffalo veterans hospital, and in 1960 a device was implanted into a 77-year-old man who lived for a further 18 months. In the same year, nine more patients, two of them children, received implants. The devices were built under licence by Medtronic, a leading US manufacturer.

However, Greatbatch was concerned that the zinc-mercury batteries needed to be changed surgically every two years. In the late 1960s he acquired rights to a newly developed lithium-iodine battery, and by 1972 his pacemakers lasted 10 years or more. Variable pacemakers, which allowed near-normal exercise, were developed in Britain in the 1980s. Greatbatch Inc is now a world-leading medical device company, and the most successful producer of pacemakers in the US.

Greatbatch was born in Buffalo, the son of a builder who had emigrated from Britain. He was an amateur radio enthusiast in childhood. During the second world war, he worked in electronics, telecommunications and radar for the US navy, and as a rear gunner and chief radio operator in the airforce.

He married Eleanor Wright and worked as a telephone repairer for a year, until, with the help of the GI bill, he took a degree in electrical engineering at Cornell University, New York state (1950), supplementing his income by running the university's radio transmitter and the electronics for their radio telescope. He then gained his MSc at Buffalo, and stayed in the city to teach part-time and work for the Taber Instrument Corporation, which declined to back his pacemaker development.

He held 330 patents, including one for a solar-powered canoe in which he paddled 160 miles when he was 72. The implantable pacemaker was named in 1983 as one of the 10 greatest engineering contributions to society by the US National Society of Professional Engineers.

Greatbatch never stopped "tinkering", as he called it. He saw invention as an end in itself: "Nine things out of 10 don't work – the tenth will pay for the other nine." His Presbyterian upbringing and wartime survival as a rear gunner made him deeply religious, and he saw a divine hand in his work. Any failure was a sign from God contributing to future success.

He experimented with biofuels, and funded work on helium-based fusion as a power source. In a 2007 interview he said: "I'm beginning to think I may not change the world but I'm still trying."

Eleanor died earlier this year. He is survived by a daughter and three sons. A fourth son predeceased him.

• Wilson Greatbatch, inventor, born 6 September 1919; died 27 September 2011